# @Version : 1.0
# @Author  : 刘宇
# @File    : 09_recursion_exercise03.py
# @Time    : 2025/10/10 12:14

def fuc(n):
    if n == 1:
        return 3
    else:
        return 2 * fuc(n - 1) + 1


print(fuc(2))


